Mathematical models for EMG force relationships in the presence of movement will be developed by both experimental and analytical methods. A coordinated series of experimental studies will be used to elucidate the major factors involved in the EMG force relationship in order to obtain necessary parameter values and functional relationships for the mathematical model. The experimental results will be used in computer simulation with system identification methods to effect a synthesis of the mathematical model. The resulting nonlinear differential equation model will be validated using experimental EMG/measurement data. Extension of the human knee will be used as the test vehicle for both the experimental and mathematical portions of the study. Definitive studies of EMG data collection; processing and quantification will underlie most other parts of the study. Their aim will be to provide standardized methodology for quantitative electromyography, while yielding the date needed for development of mathematical models. The other basic studies will be concerned with comparison of electrodes, the effect of fatigue, periarticular tissue resistance, and antagonistic muscle activity.